1. Field of the Invention
The present invention relates to a controllable current source, often also designated a “charge pump”, in an integrated circuit, comprising
a first and a second supply terminal for the application of a first and a second supply potential respectively, and
an output terminal for the delivery of an output current, connected via a first controllable current path with the first supply terminal, and via a second controllable current path with the second supply terminal.
Furthermore the invention concerns integrated circuit arrangements in which a current source of this kind is used.
2. Description of the Prior Art
A controllable current source is for example from EP 1 037 366 A2 of known art, and comprises two supply terminals for the application of two supply potentials as well as an output terminal for the delivery of an output current, wherein the output terminal is connected via a first controllable current path with the first of the supply terminals and via a second controllable current path with the second of the two supply terminals.
The task for a current source of this kind consists in providing at an output terminal an output current that is dependent on input signals (current control signals), and can be positive or negative, i.e. can flow in or out of the output terminal. The current control signals often take the form of two digital voltage signals, wherein one of the signals (“up signal”) is activated to deliver a positive current and the other current control signal (“down signal”) is activated to deliver a negative current.
A general disadvantage of current sources of known art of this kind consists in the fact that even in the switched-out state a more or less large leakage current flows via their current paths and an ensuing leakage current difference distorts the output signal. In the current source of known art from EP 1 037 366 A2 an additional disadvantage consists in that in each case to form the controllable current paths a series circuit of transistors is provided such that the circuit arrangement requires a relatively large supply voltage (difference between the two supply potentials). The trend in microelectronic circuits, however, is towards ever-smaller supply voltages.